INTRODUCTION:It has been suggested that most of the patients with bipolar disorders (BD) have either parent sidewhich is mentally ill. Furthermore, 25-27% of the children have been affected by BD if either parentside has BD, or 50-75% is affected if theboth sides of parents have BD, respectively. Heritability ofBD in monozygotic twins is 40-70%, and it is 20% in dizygotic twins. Therefore we aimed to studyhereditary issues of patients with bipolar disorders.PURPOSE:To assess hereditary issues of patients with bipolar disorders.MATERIALS AND METHODS:The study sample comprises 31 male, 81 female patients referred to the inpatient settings of theNational Center for Mental Health. The participiants were examined by psychiatric interviewsincluding objective and subjective anamnesis to assess hereditary history of bipolar disorders.Pearson’s x2 test was used for the analysis between categorical variables, whereas simple logisticregression was used for the regression analysis.RESULTS:We covered 31 male (24.8%), 81 female (75.2%) participants between 14-62 years old, mean age:42.05±0.97. Among the participants, 60 (53.6%) of them were with the hereditary history of mentaldisorders whose father (11.6%), mother (25%), a sibling (21.7%),close relatives (38.3%), and a child(3.3%) were mentally ill. 46.7% of the relatives were diagnosed with mood disorders and 36.7% ofthem were diagnosed with schizophrenia and its spectrum disorders. Furthermore, there was anassociation between mental illness of a sibling and bipolar disorders. Also, the number of patientswith BD whose mother was diagnosed with BD (13%) is more prevalent than the patients with BDwhose mother or father or other relatives were diagnosed with any mental disorders (x2 test, P value= 0.012).CONCLUSION:Heritability of BD might be associated with autosomal dominant inheritance with incompletephenotype, and mostly relevant if the patient’s sibling is diagnosed with mental disorders. Keywords:bipolar disorders, depression,mania, heredity, risk factors.